Fix another copy-paste mistake in calculateScrollPos

Issue #2819

Author: marijnh

lib/codemirror.js

@@ -3770,7 +3770,7 @@
     var screenleft = cm.curOp && cm.curOp.scrollLeft != null ? cm.curOp.scrollLeft : display.scroller.scrollLeft;
     var screenw = display.scroller.clientWidth - scrollerCutOff - display.gutters.offsetWidth;
     var tooWide = x2 - x1 > screenw;
-    if (tooWide) x2 = x1 + screen;
+    if (tooWide) x2 = x1 + screenw;
     if (x1 < 10)
       result.scrollLeft = 0;
     else if (x1 < screenleft)